Injection treatment simulation using condensation

Abstract

An injection treatment on a subterranean zone is simulated by modeling physically separate rock blocks of the subterranean zone by separate block models. The block model for each physically separate rock block represents intra-block mechanics of the rock block by finite element method. Condensation is performed in the finite element method to reduce nodal degrees of freedom operation on by the finite element method. Interactions between adjacent pairs of the rock blocks are modeled by separate joint models. The joint model for each adjacent pair of rock blocks represents inter-block mechanics between the adjacent rock blocks. The injection treatment of the subterranean zone is simulated with the block models and the joint models.

What is claimed is: 
     
       1. A computer-implemented method of simulating an injection treatment, the method comprising:
 modeling physically separate rock blocks of a subterranean zone by separate block models, the block model for each physically separate rock block representing intra-block mechanics of the rock block by a finite element method and comprising performing condensation in the finite element method to reduce nodal degrees of freedom operated on by the finite element method; 
 modeling interactions between adjacent pairs of the rock blocks by separate joint models, the joint model for each adjacent pair of rock blocks representing inter-block mechanics between the adjacent rock blocks; and 
 simulating, by a data processing apparatus, an injection treatment of the subterranean zone with the block models and the joint models. 
 
     
     
       2. The method of  claim 1 , wherein performing condensation in the finite element method comprises performing the finite element method using only a subset of the degrees of freedom of the finite element mesh. 
     
     
       3. The method of  claim 1 , wherein performing condensation in the finite element method comprises performing Guyan condensation. 
     
     
       4. The method of  claim 1 , wherein performing condensation in the finite element method comprises performing condensation on a plurality of the block models in parallel. 
     
     
       5. The method of  claim 1 , wherein the joint model for each adjacent pair of rock blocks represents inter-block mechanics between the adjacent rock blocks as predefined inter-block joints. 
     
     
       6. The method of  claim 1 , wherein one or more of the adjacent pairs of rock blocks contact each other at physical contact locations, and the joint model for each adjacent pair of rock blocks represents inter-block forces between the rock blocks at predefined joint model locations that are different from the physical contact locations. 
     
     
       7. The method of  claim 1 , wherein the joint model for each adjacent pair of rock blocks represents all inter-block forces between the rock blocks as equivalent forces acting at two predefined joint model locations. 
     
     
       8. The method of  claim 1 , wherein simulating an injection treatment includes simulating time-evolution of the rock blocks and their interactions during an injection treatment applied to the subterranean zone. 
     
     
       9. The method of  claim 1 , wherein simulating an injection treatment includes simulating fluid flow in and about the rock blocks during an injection treatment applied to the subterranean zone. 
     
     
       10. The method of  claim 1 , wherein the block model for each rock block represents intra-block mechanics of the rock block in response to inter-block forces determined by the joint models. 
     
     
       11. The method of  claim 1 , wherein the joint model for each adjacent pair of rock blocks represents inter-block mechanics between adjacent rock blocks in response to rock block movement determined by the block models. 
     
     
       12. A non-transitory computer-readable medium storing instructions that, when executed by a data processing apparatus, perform operations comprising:
 modeling physically separate rock blocks of a subterranean zone by separate block models, the block model for each physically separate rock block representing intra-block mechanics of the rock block by a finite element method and comprising performing condensation in the finite element method to reduce nodal degrees of freedom operated on by the finite element method; 
 modeling interactions between adjacent pairs of the rock blocks by separate joint models, the joint model for each adjacent pair of rock blocks representing inter-block mechanics between the adjacent rock blocks; and 
 simulating an injection treatment of the subterranean zone with the block models and the joint models. 
 
     
     
       13. The computer-readable medium of  claim 12 , wherein performing condensation in the finite element method comprises using only a subset of the degrees of freedom of the finite element mesh. 
     
     
       14. The computer-readable medium of  claim 12 , wherein performing condensation in the finite element method comprises performing Guyan condensation. 
     
     
       15. The computer-readable medium of  claim 12 , wherein performing condensation in the finite element method comprises performing condensation on a plurality of the block models in parallel. 
     
     
       16. The computer-readable medium of  claim 12 , wherein one or more of the adjacent pairs of rock blocks contact each other at physical contact locations, and the joint model for each adjacent pair of rock blocks represents inter-block forces between the rock blocks at predefined joint model locations that are different from the physical contact locations. 
     
     
       17. The computer-readable medium of  claim 12 , wherein simulating an injection treatment includes simulating fluid flow in and about the rock blocks during an injection treatment applied to the subterranean zone. 
     
     
       18. An injection treatment simulation system comprising one or more computers configured to perform operations comprising:
 modeling physically separate rock blocks of a subterranean zone by separate block models, the block model for each physically separate rock block representing intra-block mechanics of the rock block by a finite element method and comprising performing condensation in the finite element method to reduce nodal degrees of freedom operated on by the finite element method; 
 modeling interactions between adjacent pairs of the rock blocks by separate joint models, the joint model for each adjacent pair of rock blocks representing inter-block mechanics between the adjacent rock blocks; and 
 simulating an injection treatment of the subterranean zone with the block models and the joint models. 
 
     
     
       19. The injection treatment system of  claim 18 , wherein performing condensation in the finite element method comprises performing the finite element method using only a subset of the degrees of freedom of the finite element mesh. 
     
     
       20. The injection treatment system of  claim 18 , wherein performing condensation in the finite element method comprises performing Guyan condensation. 
     
     
       21. The injection treatment system of  claim 18 , wherein performing condensation in the finite element method comprises performing condensation on a plurality of the block models in parallel. 
     
     
       22. The injection treatment simulation system of  claim 18 , wherein the joint model for each adjacent pair of rock blocks represents inter-block mechanics between the adjacent rock blocks as predefined inter-block joints. 
     
     
       23. The injection treatment simulation system of  claim 18 , wherein one or more of the adjacent pairs of rock blocks contact each other at physical contact locations, and the joint model for each adjacent pair of rock blocks represents inter-block forces between the rock blocks at predefined joint model locations that are different from the physical contact locations. 
     
     
       24. The injection treatment simulation system of  claim 18 , wherein the block model for each rock block represents intra-block mechanics of the rock block in response to inter-block forces determined by the joint models. 
     
     
       25. The injection treatment simulation system of  claim 18 , wherein the joint model for each adjacent pair of rock blocks represents inter-block mechanics between adjacent rock blocks in response to rock block movement determined by the block models.